Advances in electronic technology cause integrated circuits to be formed on substrates such as silicon wafers with ever increasing packing density of active components. The formation of circuits is carried out by sequential application, processing, and selective removal of various materials from the substrate. Various compositions have been developed for removal of specific classes of materials from substrates in semiconductor wafer technologies. For example, a composition commonly denoted SC-1, which contains a mixture of NH4OH (29 wt %)/H2O2 (30 wt %)/water at a volume ratio of about 1:1:5 (or at somewhat higher dilution ratios), is typically used to remove particles and to reoxidize hydrophobic silicon surfaces. Similarly, a composition commonly denoted SC-2, which contains a mixture of HCl (37 wt %)/H2O2 (30 wt %)/water at a volume ratio of about 1:1:5 (or at somewhat higher dilution ratios), is typically used to remove metals. An additional composition, commonly called a Piranha composition, comprises H2SO4 (98 wt %)/H2O2 (30 wt %) at a volume ratio of about 2:1 to 20:1, and is typically used to remove organic contamination or some metal layers.
Removing materials, and preferably photoresist, from a substrate is described in U.S. Pat. No. 7,592,264. In this patent, a liquid sulfuric acid composition comprising sulfuric acid and/or its desiccating species and precursors and having a water/sulfuric acid molar ratio of no greater than 5:1 is dispensed onto an material coated substrate in an amount effective to substantially uniformly coat the material coated substrate. The substrate is preferably heated to a temperature of at least about 90° C., either before, during or after dispensing of the liquid sulfuric acid composition. After the substrate is at a temperature of at least about 90° C., the liquid sulfuric acid composition is exposed to water vapor in an amount effective to increase the temperature of the liquid sulfuric acid composition above the temperature of the liquid sulfuric acid composition prior to exposure to the water vapor. The substrate is then preferably rinsed to remove the material.
A method of treating a substrate is described in U.S. Pat. No. 7,819,984, whereby a substrate having material on a surface thereof is placed in a treatment chamber and a stream of a liquid treatment composition is directed to impinge the substrate surface with a stream of water vapor directed to impinge the substrate surface and/or to impinge the liquid treatment composition.
Silicon nitride is used as a mask material in the formation of various devices. In these processing techniques, the silicon nitride mask is selectively removed by etching as compared to other materials in place on the substrate, and particularly silicon oxide. Submersion of the substrate comprising silicon nitride in a bath of boiling H3PO4 has been used as an etching process for such applications, due to a selectivity of about 35:1 etching of silicon nitride as compared to silicon dioxide. In order to provide control of the selectivity and etch rate, such baths are pre-conditioned by first seasoning the bath with sacrificial silicon nitride coated wafers in incorporate silica into the bath at a desired level. A method of avoiding such seasoning of the bath is described in A. L. P. Rotondaro et al., “USE OF H2SO4 FOR ETCH RATE AND SELECTIVITY CONTROL OF BOILING H3PO4,” Electrochemical Society Proceedings Volume 99-36, page 385-390 (1999), wherein the etch rate and selectivity of a phosphoric acid bath is improved by addition of sulfuric acid to the bath.
It would be desirable to identify alternative techniques and compositions for treatment of substrates, particularly to remove nitride materials, especially silicon nitride, from substrates such as semiconductor wafers.